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Dec 10, 2025

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7 pages

Digestive System Components and Functions Notes

andi :]

@snuggly_bunbun

The digestive system is a complex network of organs working... Show more

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Digestive System Column Notes
Topic
Organs of the
Alimentary
Canal
(Gastrointestinal
(GI Tract))
Mouth (Oral
Cavity)
Notes
● Hollow tube tha

The Mouth and Oral Cavity

Your digestive journey begins in your mouth, the entrance to the digestive system. When you take a bite of food, it enters a specially designed space with several important parts: lips that protect the opening, cheeks forming the sides, and both hard and soft palates forming the roof.

The star of the mouth is your tongue, which sits on the floor of your mouth attached by the lingual frenulum (that little piece of tissue under your tongue). Your tongue does more than just help you talk—it mixes food with saliva and helps you swallow. The surface of your tongue contains papillae which house your taste buds, making food enjoyable rather than just fuel.

Other important structures include your tonsils (which can become inflamed and make swallowing difficult) and the uvula (that dangling piece at the back of your throat). If someone is "tongue-tied," it means they have a short lingual frenulum that can affect speech and may need to be surgically corrected.

Did you know? The uvula isn't just a random piece of tissue—it helps prevent food from going up into your nasal cavity when you swallow and plays a role in your gag reflex!

The Pharynx and Esophagus

After you swallow, food moves into your pharynx (throat), which has three sections: the nasopharynx (part of your respiratory system), the oropharynx (connected to your mouth), and the laryngopharynx (which leads to your esophagus). The food then travels down your esophagus, a muscular tube connecting your throat to your stomach.

Food doesn't just fall down your esophagus—it's actively pushed along by peristalsis, a wave-like motion created by alternating contractions of two muscle layers. This important process ensures food keeps moving in the right direction.

The digestive tract from the esophagus onward has four main tissue layers that work together. From inside to outside: the mucosa (innermost lining), submucosa (soft connective tissue), muscularis externa (muscle layers that create peristalsis), and serosa (the outer protective layer). These layers are critical for both protection and function.

Watch out! If bacteria enter the peritoneal cavity (the space around your digestive organs), you can develop peritonitis. Your body initially tries to contain the infection by causing the peritoneal membranes to stick together, but medical attention is needed to resolve it.

The Stomach

Your stomach is much more than just a food bag—it's a temporary storage tank with specialized regions. The fundus at the top, the main body in the middle, and the pylorus at the bottom where most digestion happens. Food enters through the cardioesophageal sphincter and exits as chyme (partially digested food) through the pyloric sphincter.

The stomach has two protective structures called omentums. The lesser omentum connects the stomach to the liver, while the greater omentum acts like a protective blanket over your abdominal organs. This greater omentum not only cushions your organs but contains defensive cells from your immune system.

Your stomach digests food in two ways. Mechanically, the strong muscles of the muscularis externa churn and break food into smaller fragments. Chemically, the stomach lining (made of simple columnar epithelium) contains millions of gastric pits with specialized cells. Chief cells produce pepsinogens, parietal cells create hydrochloric acid (making the stomach acidic), and enteroendocrine cells release helpful digestive hormones.

Amazing fact: Your stomach protects itself from being digested by its own powerful acids! The mucosa produces a thick layer of protective mucus that prevents the stomach from essentially digesting itself.

The Small Intestine

The small intestine is the digestive superstar—it's where most digestion occurs and nutrients are absorbed into your bloodstream. This long tube connects the stomach to the large intestine and has three main sections: the duodenum, jejunum, and ileum.

In the duodenum, digestive juices from the pancreas and liver enter through ducts to help break down food. The pancreas provides enzymes that complete chemical digestion, while the liver supplies bile to process fats. These important fluids enter the duodenum together through joined ducts.

The small intestine has amazing adaptations to maximize absorption. Its walls contain microvilli (tiny projections with digestive enzymes), villi $finger-like projections containing blood vessels and lymphatic capillaries called lacteals$ , and circular folds that increase surface area. The walls also contain Peyer's patches—collections of lymphatic tissue that prevent bacteria from entering your bloodstream.

Cool structure alert: If you could unfold all the surface area in your small intestine (including villi and microvilli), it would cover a tennis court! This massive surface area ensures you absorb as many nutrients as possible from your food.

The Large Intestine

After nutrients are absorbed in the small intestine, what's left moves into the large intestine, which focuses on absorbing water and forming waste (feces). This final section of the digestive tract has several parts working together.

The journey through the large intestine begins at the cecum, a pouch-like structure with the appendix attached (which can become infected, causing appendicitis). Food then travels through the colon, which has four sections: ascending (up), transverse (across), descending (down), and sigmoid $S-shaped$ . Finally, waste is stored in the rectum before leaving the body through the anus, which has both voluntary and involuntary sphincters.

The large intestine has special features that help with its functions. Goblet cells produce mucus to lubricate feces as it moves through, making elimination easier. The muscle layer of the large intestine typically stays contracted, creating small pouches called haustra that characterize its appearance.

Name origin: The sigmoid colon gets its name from its distinctive S-shape—"sigmoid" comes from the Greek letter sigma (σ), which in its ancient form resembled an S!

Accessory Digestive Organs: Salivary Glands and Pancreas

Your salivary glands produce saliva that starts the digestive process in your mouth. Saliva contains mucus, serous fluids, salivary amylase (an enzyme that breaks down starch), lysozyme, and antibodies that fight bacteria. This mixture moistens food for easy chewing and swallowing, begins starch digestion, inhibits harmful bacteria, and dissolves food chemicals so you can taste them.

You have three pairs of major salivary glands. The parotid glands sit in your cheeks and can become inflamed with mumps. The submandibular glands and sublingual glands both empty through ducts into the floor of your mouth.

The pancreas has dual roles in digestion. It produces powerful enzymes that break down all types of food particles (proteins, carbohydrates, and fats), which are secreted into the duodenum in a neutralizing fluid. It also produces the hormones insulin and glucagon, which regulate blood sugar levels.

Health note: Mumps, an inflammation of the parotid glands, was once a common childhood disease that made opening the mouth and chewing painful. Thanks to vaccines, mumps is now much less common in developed countries.

The Liver and Gallbladder

Your liver is a digestive powerhouse that produces bile, a greenish fluid that emulsifies fats—breaking them into tiny droplets that are easier for enzymes to process. Bile contains bile salts, bile pigments (bilirubin), cholesterol, phospholipids, and electrolytes. It travels from the liver to the duodenum through the common hepatic duct and bile duct.

Several liver conditions can affect digestion. Jaundice occurs when bile builds up in the bloodstream (turning skin yellow) due to blocked ducts. Hepatitis is inflammation of the liver, often caused by viral infections. Cirrhosis involves severe liver damage, typically from excessive alcohol consumption or advanced hepatitis.

The gallbladder stores and concentrates bile when you're not eating. When fatty foods enter your duodenum, the gallbladder receives signals to release bile through the cystic duct. Sometimes cholesterol in bile can crystallize, forming sharp, painful gallstones. This typically happens when bile stays in the gallbladder too long or becomes too concentrated.

Clarification: Despite common belief, vomit isn't actually bile. What people call "bile" when they throw up is usually stomach acid and partially digested food. True bile is typically only seen in vomit after extended, severe vomiting when the duodenal contents get pushed backward.

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Biology

•

Dec 10, 2025

•

7 pages

Digestive System Components and Functions Notes

andi :]

@snuggly_bunbun

Clarification: Despite common belief, vomit isn't actually bile. What people call "bile" when they throw up is usually stomach acid and partially digested food. True bile is typically only seen in vomit after extended, severe vomiting when the duodenal contents get pushed backward.